The role of wild birds in the ecology of avian influenza: ten years of research at CIRAD

09/2015

Right from the start of the avian influenza epidemic, CIRAD teams began working on the surveillance of the H5N1 virus in wild birds, particularly in Africa. Thanks to the fieldwork and also to the theoretical research done by those teams, we now know a little more about this disease, which can be transmitted to humans. Among other things, we know that the viruses are sustained all year round in Africa, we know the main species involved in that persistence and we can assess the epidemiological and ecological contexts in which the disease develops better. This work has paved the way for new control methods and highlights the need for global surveillance.

More is now known about the role of wild birds in the ecology of avian influenza virus transmission, although some aspects of their involvement in the epidemiological cycle of infection remain to be determined.

It is particularly important that we elucidate their role now, since there has been an increase in the number of highly pathogenic avian influenza (HPAI) epizootics since late 2014, with a record number of cases of infection in humans (140) by the highly pathogenic H5N1 virus since 2003.

The virus has also reappeared in poultry and wild birds in West Africa, the Middle East and Eastern Europe, whereas there had not been any infections in those regions for several years.

New H5-type strains of the HPAI virus resulting from a cross between Eurasian and American strains have also been seen for the first time this year in North America, where they have had a substantial health and economic impact poultry farms.

Vital field research

In 2005, researchers from CIRAD began studying avian influenza viruses in wild birds, notably in Africa. At the time, there were next to no data on their role in circulating the disease, hence there was no way of establishing epidemiological patterns.

Thanks to the work done by CIRAD and the GRIPAVI project it coordinated, we know that the viruses persist all year round in Africa and also know the main species involved in that persistence.

This fieldwork also served to determine the risk of avian influenza transmission between wild and domestic birds, and enabled proposals for managing that risk. It was an opportunity to gather large amounts of data, and also to draft and test disease epidemiology hypotheses.

It has brought CIRAD scientific recognition that means it is now involved in global avian influenza networks and plays a role in the global debate on the disease.

As the fruit of this empirical and theoretical research, a series of articles was published recently by CIRAD researchers, shedding new light on the disease.

Standardizing data gathering

In a recent article, researchers launched an appeal for data gathering on influenza in wild birds to be standardized, and for the global efforts being made in this field to be sustained.

This is vital with a view to establishing sanitary surveillance, which will serve to collect all the virus strains found in wildlife that could contaminate poultry and humans.

Putting the issue in context

The multidisciplinary approaches taken by CIRAD and its international partners have also enabled it to put the avian influenza issue in context as regards the various socio-ecosystems in which it occurs.

In fact, epidemiological and ecological contexts differ from one region to another. Researchers therefore recommend taking a systemic approach in order to pinpoint the variability of eco-epidemiological systems and understand the factors that influence them better.

Bridge species, a new epidemiological function

Researchers have also precisely defined a new epidemiological function: "bridge species", species capable of connecting a population within which the virus persists, for instance wild ducks, and a naive population that has never been in contact with the disease and that it is important to protect, such as chickens.

They have pinpointed previously overlooked species such as swallows and passerines, capable of acting as a disease transmission relay. This discovery paves the way for a new disease control method: limiting contact between domestic birds and bridge species. As a way of restricting avian influenza transmission, this is much easier than controlling the disease in wild ducks.